[PATCH net-next 1/4] net: dsa: don't offload switchdev objects on ports that don't offload the bridge

[Vladimir Oltean <olteanv@gmail.com>]

From: Vladimir Oltean <vladimir.oltean@nxp.com>

Starting with commit 058102a6e9eb ("net: dsa: Link aggregation support"),
DSA warns that certain configurations of upper interfaces are not offloaded
to hardware. When a DSA port does not offload a LAG interface, the
dp->lag_dev pointer is always NULL. However the same cannot be said about
offloading a bridge: dp->bridge_dev will get populated regardless of
whether the driver can put the port into the bridge's forwarding domain
or not.

Instead of silently returning 0 if the driver doesn't implement
.port_bridge_join, return -EOPNOTSUPP instead, and print a message via
netlink extack that the configuration was not offloaded to hardware.

Now we can use the check whether dp->bridge_dev is NULL in order to
avoid offloading at all switchdev attributes and objects for ports that
don't even offload the basic operation of switching. Those can still do
the required L2 forwarding using the bridge software datapath, but
enabling any hardware features specific to the bridge such as address
learning would just ask for problems.

Signed-off-by: Vladimir Oltean <vladimir.oltean@nxp.com>
---
 net/dsa/dsa_priv.h | 2 ++
 net/dsa/slave.c    | 5 +++++
 net/dsa/switch.c   | 7 +++++--
 3 files changed, 12 insertions(+), 2 deletions(-)

diff --git a/net/dsa/dsa_priv.h b/net/dsa/dsa_priv.h
index f5949b39f6f7..7b0dd2d5f3f8 100644
--- a/net/dsa/dsa_priv.h
+++ b/net/dsa/dsa_priv.h
@@ -205,6 +205,8 @@ static inline bool dsa_port_offloads_netdev(struct dsa_port *dp,
 					    struct net_device *dev)
 {
 	/* Switchdev offloading can be configured on: */
+	if (!dp->bridge_dev)
+		return false;
 
 	if (dev == dp->slave)
 		/* DSA ports directly connected to a bridge, and event
diff --git a/net/dsa/slave.c b/net/dsa/slave.c
index 8c9a41a7209a..94bce3596eb6 100644
--- a/net/dsa/slave.c
+++ b/net/dsa/slave.c
@@ -1922,6 +1922,11 @@ static int dsa_slave_changeupper(struct net_device *dev,
 			err = dsa_port_bridge_join(dp, info->upper_dev);
 			if (!err)
 				dsa_bridge_mtu_normalization(dp);
+			if (err == -EOPNOTSUPP) {
+				NL_SET_ERR_MSG_MOD(info->info.extack,
+						   "Offloading not supported");
+				err = 0;
+			}
 			err = notifier_from_errno(err);
 		} else {
 			dsa_port_bridge_leave(dp, info->upper_dev);
diff --git a/net/dsa/switch.c b/net/dsa/switch.c
index 1906179e59f7..4137716d0de5 100644
--- a/net/dsa/switch.c
+++ b/net/dsa/switch.c
@@ -88,9 +88,12 @@ static int dsa_switch_bridge_join(struct dsa_switch *ds,
 {
 	struct dsa_switch_tree *dst = ds->dst;
 
-	if (dst->index == info->tree_index && ds->index == info->sw_index &&
-	    ds->ops->port_bridge_join)
+	if (dst->index == info->tree_index && ds->index == info->sw_index) {
+		if (!ds->ops->port_bridge_join)
+			return -EOPNOTSUPP;
+
 		return ds->ops->port_bridge_join(ds, info->port, info->br);
+	}
 
 	if ((dst->index != info->tree_index || ds->index != info->sw_index) &&
 	    ds->ops->crosschip_bridge_join)
-- 
2.25.1